Conventionally, there is known a visible light communication apparatus (illumination apparatus) which includes light emitting diodes (LEDs) as a light source and transmits a signal by modulating the intensity of illumination light (see, e.g., Japanese Unexamined Patent Application Publication No. 2013-110634). In the visible light communication apparatus, since the signal is transmitted by modulating the illumination light itself, there is no need for a special device as in an infrared communication device. Further, since power saving can be achieved by using light emitting diodes as the light source, it is being studied to use the visible light communication apparatus in a ubiquitous information system for the underground shopping district or the like.
The visible light communication apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2013-110634 includes a resistor connected in series to the light emitting diodes and a switching element connected in parallel to the resistor. Further, by controlling the turning-on and the turning-off of the switching element in response to a communication signal, and modulating the light intensity of the light emitting diodes, the communication signal is superimposed on the illumination light outputted from the light emitting diodes.
Generally, if a current flowing through the light emitting diodes is small, the light emitting diodes has characteristics that a resistance value of the equivalent resistance of the light emitting diodes increases. Therefore, during dimming of the light emitting diodes in which the current supplied to the light emitting diodes is small, there is a possibility that a modulation degree decreases and a communication error occurs.